1. Field
This document relates to a switchable Fresnel lens and a fabrication method thereof.
2. Discussion of the Related Art
As the stereoscopic image reproduction technology is applied to display devices, such as a television or a monitor, now is the age in which people can view 3D stereoscopic images even at home. A stereoscopic image display may be divided into a wearable glasses-type and a no glasses type. The glasses-type displays are configured to display left and right parallax images on a direct-view display or projector by changing polarization direction thereof or in a time-divisional manner. In this way, the glasses-type display implements a stereoscopic image using polarization glasses or liquid-crystal shutter glasses. For the no glasses type, the display may include optical parts, such as a parallax barrier and a lens, for separating the optical axes of left and right parallax images. In this way, the no glasses type of display may be installed in front of or behind a display screen.
FIG. 1 shows an example of a no glasses type stereoscopic image display device using a lens.
Referring to FIG. 1, the no glasses type stereoscopic image display device comprises a lens LENS placed in front of a pixel array PIX of a display panel. The lens LENS separates the optical axis of light from pixels to which a left-eye image L is written and the optical axis of light from pixels to which a right-eye image R is written. While the viewer sees the pixels with the left-eye image L written thereto, with the left eye through the lens LENS, the viewer sees the pixels with the right-eye image written thereto, with the right eye through the lens LENS, thus allowing the viewer to perceive a binocular parallax and view a stereoscopic image. The thickness t of the lens LENS having the structure shown in FIG. 1 is large.
The lens LENS is generally implemented as a convex lenticular lens array whose cross section is hemispherical or elliptical, as illustrated in FIG. 1. A method of implementing the lens LENS as a switchable lens sealed with liquid crystal has been recently proposed. The switchable lens is formed by applying an electric field to liquid crystal molecules through electrodes and changing the refractive index of the liquid crystal molecules, and makes it easy to switch between 2D mode and 3D mode by controlling the driving voltage applied to the electrodes. For example, the present applicants have proposed a switchable barrier and a switchable lens in U.S. patent application Ser. No. 13/077,565 (2011 Mar. 1) and Ser. No. 13/325,272 (2011 Dec. 14). However, even if the lens LENS is implemented as a switchable lens, a cell gap becomes thicker due to the thickness of the lens which is undesirable.